Zimmerman wasn't a "case-by-case basis". It was a highly publicized trial that garnered nationwide attention and was "the talking point" for several months. Those are the kinds of cases that shift public opinion if the outcome of the case was "dude, you fucking ran into a completely random person and automatically assumed he was a "thug" based on his demeanor and ended up killing him. Do you realize how racist and NOT OK this is?"
"We need to work on it as a society" says nothing. Again, it's an easy out. Yes we should all hold hands and have giant circle discussions encompassing entire cities for us to "work on it as a society". Oh but that doesn't happen. Darn. I guess back to the status quo we go. Very easy to make vague sweeping statements about how entire cultures should somehow make fundamental changes in the ways it views its own forms of institutionalized racism with no specifics whatsoever. It's this mentality that makes every single case feel like a "drop in the ocean". Oh this exact particular case won't suddenly shift a culture's viewpoint, so let's not bother. This next one? Same thing, let's not bother either. The one 4 years from now? Another drop, who cares. The one 10 years from now? Same. But if you did the opposite, if you grabbed every single case by the throat and showed, publicly, why this racially motivated incident was racially motivated, why this even happened in the first place, and why this shouldn't be happening, and if you keep doing it again and again, for this case, for the next, the one in 4 years, and the one in 10, you bet your ass you're going to start seeing a cultural shift. This is exactly why "movements" happen, to make a sustained effort to shatter the status quo.
But, in fact, what your'e not realizing is that pointing out the racial issues with cases like this would've actually been "working it out as a society", because this is what happens in a society. It was the microcosm of people's racial profiling, the trigger-happy nature of many dim-witted gun supporters, that was the background of this very high profile case. You make a clear statement in this platform, you take a small step into ending this status quo of subtle but equally hurtful racist undertones of many aspects of society. If you fail to do this, you take a small step in the opposite direction. Kicking the can down the road and waiting for some other incident so that we can maybe start making a serious effort gets absolutely nowhere, as is saying stuff like "it's about culture. We should change culture" with no further specifics of discussion provided whatsoever.